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I placed a stainless steel idli stand in a pressure cooker (unsure if the cooker is Aluminium or steel, but it has the word "wrought" etched on its worn out bottom), poured some water into the cooker (the water was pre-boiled in a stainless steel saucepan on an induction cooker) and steamed some idlis. After steaming, I see this dark something at the bottom of the cooker, everywhere except where the idli stand was placed (the lighter coloured circle).
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This is what the idli stand looks like:
enter image description here
And this is what the pressure cooker looks like:
enter image description here

Questions:

  1. Did the stain (or perhaps it's not a stain. Perhaps it's a layer that got eroded) get created as a result of the reaction with the metals and water? What causes it? There's also a very thin white layer that gets created on the portion of the idli stand which is immersed in water.
  2. How do I get rid of the discolouration? Already tried using a liquid dishwashing agent. Didn't work. Tried a bit of vinegar and baking soda too. No use.
  3. Is it safe to cook using the pressure cooker, in its current state?

Update1:
From a few searches, it could be:

Update2:
When I float an Aluminium container on the water in the pressure cooker, a white layer develops on the container. The white layer had also developed on the portion of the idli stand that was immersed in water. Am assuming it's some minerals dissolved in the water. enter image description here

2 Answers 2

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My guess from what is shown is a carbonaceous material from some organic burned in the pan. Likely can only be removed mechanically/( eg scraping, scrubbing). It is not harmful. You did not effect the stainless surface with cooking temperatures ( did not add to the normal chrome oxide). Your stainless pressure cooker may have an aluminum core.

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  • I cooked rice in the pressure cooker, and some of that dark layer seems to have gone away. There was no problem with the rice colour. I've updated the question with one more image. I think the water has too much of minerals dissolved in it. Possibly borewell water being mixed into the corporation water.
    – Nav
    Feb 15, 2023 at 6:50
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From the surface looks of your container, this looks more like aluminum than stainless steel. Aluminum pretty much always gets this kind of discoloration with use. I don't know what causes it, but I think it's just par for the course when using aluminum.

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  • You may be right. I see there's a stainless steel version of it too. As of now I'm placing a prop below the idli stand to prevent it from causing the discolouration.
    – Nav
    Sep 27, 2023 at 12:20
  • You are right. It is Aluminium. When I scraped off rice stuck to the bottom using a stainless steel spoon, it left scratch marks.
    – Nav
    Dec 16, 2023 at 17:56

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